Abstract：According to the multi-supported structure feature of high-speed flexible rotor and with the demand of rotor dynamic design, the influence of the bearing looseness on the rotor dynamic was analyzed. The nonlinear vibration response characteristics of the high-speed flexible rotor system were obtained through simulation. The results show that when the working speed of rotor is above the critical speed, the periodic, quasi-periodic and chaos can exist when the flexible rotor working. Furthermore, the influence of location of bearing looseness, value of unbalance and bearing clearance on the vibration response of multi-supported flexible rotor was studied. The analysis results provide theoretical method for dynamic design of multi-supported high-speed flexible rotor system.